The entire disclosure of Japanese Patent Application No. 2000-138334 filed on May 11, 2000 including specification, claims, drawings and summary is incorporated herein by reference in its entirety.
1. Field of the Invention
This invention relates to a rotary press for printing a web, and more specifically, to a rotary press adapted to prevent entrainment of a web during plate changing.
2. Description of the Related Art
Generally, this type of rotary press is composed of a feeder having a roll comprising a web wound in a roll form, a printing unit having printing cylinders, such as blanket cylinders and plate cylinders, for printing the web fed from the feeder, a dryer for drying the web printed by the printing unit, and a folder for folding the web. When changing a plate in a double-sided four-color printing press having four printing units, for example, the printing press is stopped, and the plate cylinder is rotated by about one turn in normal and reverse directions to remove the old plate from the plate cylinder and mount a new plate on the plate cylinder.
When rotating the plate cylinder in the normal and reverse by about one turn, if an as-printed state is maintained, namely, if the web is kept taut between the feeder and the dryer, a heavy load may be imposed on the web between the printing units and the dryer to cause tearing of the web. To prevent this problem, a connection between a drive on the folder side and a drive on the printing unit side is cut off by a clutch, and the printing cylinder is rotated by almost two turns in the normal direction. By this measure, the web is slackened beforehand between the printing units and the dryer.
Japanese Unexamined Patent Publication No. 165400/1999 discloses a technique which provides a wrap preventing member (press roller, dancer roller) on a web travel route between a printing unit and a folder (and between a feeder and the printing unit), the wrap preventing member being designed to retreat during printing and advance during plate changing to contact the web, so that a slack portion of the web is pressed downward and stretched under a certain tension by the wrap preventing member. According to this technique, the slack portion of the web is prevented from swaying toward the blanket cylinder or the plate cylinder during plate changing and being caught between the plate cylinder and the blanket cylinder positioned below the web.
In the rotary press of the above-described publication, the drive clutch is engaged after completion of plate changing, and the web is discharged toward the folder. However, the pressure of the wrap preventing member during plate changing is so high that the web accumulated at the wrap preventing member on the folder side cannot be discharged. Thus, the pressure of the wrap preventing member was weakened after completion of plate changing so that the web accumulated at the wrap preventing member can be discharged. However, the feed amount of the web fed from the feeder (infeed unit), and the feed amount of the web discharged toward the folder are small. Thus, it takes time to discharge the web accumulated at the wrap preventing member. Depending on the paper quality of the web, etc., moreover, the wrap preventing member still fails to ascend.
The present invention has been accomplished in consideration of the above problems with the earlier technology. It is the object of the invention to provide a rotary press in which after plate changing is completed, a wrap preventing member can smoothly ascend regardless of its pressure, and can promptly and smoothly return to the state before plate changing.
The present invention, which attains the above object, is a rotary press for printing a web fed from a feeder by a printing unit, comprising a wrap preventing member provided on a travel route for the web downstream from the printing unit, the wrap preventing member being adapted to retreat during printing and advance during plate changing to contact the web, and a pinching member provided on the travel route for the web between the feeder and the printing unit, the pinching member being adapted to support the web in a pinching manner, wherein the wrap preventing member is movable in a retreating direction by the web, with the web being supported in the pinching manner by the pinching member.
According to this aspect, after plate changing is completed, the wrap preventing member can smoothly ascend regardless of its pressure, and can promptly and smoothly return to the state in which it was in before plate changing.
The wrap preventing member may be a press roller, and may be adapted to move upward and downward in accordance with contraction and extension of an air cylinder for the press roller, the air cylinder being mounted so as to face downward.
The air cylinder for the press roller may make a contracting motion when the press roller is detected by a sensor provided at a position at which slackness of the web is small.
The press roller may be locked by a locking mechanism when the air cylinder for the press roller is maximally contracted.
A second wrap preventing member may be provided on the travel route for the web between the feeder and the printing unit and downstream of the pinching member.
The second wrap preventing member may be a second press roller, and may be adapted to move upward and downward in accordance with contraction and extension of an air cylinder for the second press roller, the air cylinder for the second press roller being mounted so as to face downward.
The air cylinder for the second press roller may make a contracting motion when the second press roller is detected by a sensor provided at a position at which slackness of the web is small.
The second press roller may be locked by a second locking mechanism when the air cylinder for the second press roller is maximally contracted.
The pinching member may be composed of a pair of plates, and at least one of the plates may be supported so as to be movable toward and away from the other of the plates.
After the wrap preventing member is brought into an advancing state, the web may be pinched by the pinching member; with a pinched state of the web being kept, plate changing may be performed by normal and reverse rotations of plate cylinders; after plate changing is completed, the wrap preventing member may be retreated by the web, and then the pinched state of the web by the pinching member may be released.
The wrap preventing member may enter into an advancing state after normal rotation of plate cylinders; then, after the plate cylinders are stopped, a second wrap preventing member, provided on the travel route for the web between the feeder and the printing unit and downstream from the pinching member, may be brought into an advancing state; then, with the web being pinched by the pinching member, plate changing may be performed by normal and reverse rotations of the plate cylinders; and after plate changing is completed, the wrap preventing member and the second wrap preventing member may be retreated by the web, and then the pinched state of the web by the pinching member may be released.